Device for measuring ground water pressure



May 9, 1967 D. sHlELDs ET A1. 3,318,140

DEVICE FOR MEASURING GROUND WATER PRESSURE Filed Feb. 23, 1965 l N VEN TORS United States Patent Office 3,318,140 Patented May 9, 1967 3,318,140 DEVICE FOR MEASURIN/G GRUND WATER PRESSURE Donald Shields, 41 Strath Ave., Toronto, ntario, Canada, and Kenneth Pealrer, 27 Bratty Road, Downsview,

Ontario, Canada Filed Feb. 23, 1965, Ser. No. 434,429 5 Claims. (Cl. 73-73) This application is a continuation-impart of my earlier file application Ser. No. 185,752, iiled Apr. 6, 1962, now abandoned.

This invention relates to an improved ground water pressure measuring device for use in measuring the pressure of water in soil.

Ground water pressure is an important factor in the engineering of construction projects involving soil excavation and/or soil placement. Advance information on ground water pressure in soil which is to be excavated enables the project to be planned to avoid problems which can result from the presence of high ground water pressures. For example, high pressure water bearing formations which could cause serious problems if encountered unexpectedly in excavating for buildings, subways and the like can be located prior to commencing the excavation and, if necessary, remedial measures, such as drilling of relief wells, can be taken. Also, it is often important to be able to ascertain the presence and pressure of ground Water which may build up in earth structures such as dams during or after their construction.

Devices are known by which ground water pressure can be measured. Generally, `these known devices consist of elongated porous ceramic or stone tubes, sealed at the top and bottom ends and provided with a conduit through the top end for transmitting pressure measurements from the interior of the tube to the surface. These ceramic tubes are positioned in a bore hole in the ground and surrounded with a layer of relatively coarse sand which acts .as a filter to prevent clogging of the pores of the ceramic tube with soil particles.

Such devices have a number of disadvantages. They are formed `of brittle material which is highly susceptible to breakage during shipping and handling on the job. They are relatively expensive and are inconvenient and time consuming to use as they must be assembled on the job -by fitting and sealing the top and bottom plugs and, when placed in the bore hole, they must .be surrounded with a layer of lter sand. The placing of the filter sand is a particularly time consuming procedure where the pressure measuring device is to be placed at a fairly substantial depth, such as thirty or forty feet in the ground. Y

It is a principal object of the present invention to provide a simple, inexpensive ground Water pressure measuring device which can be placed in bore holes in direct contact with any type of soil for the measurement of water pressure therein. A further yobject of this invention is to provide a pre-assembled, readily transportable ground water pressure measuring device which can be quickly and easily installed to give accurate measurements of ground water pressure.

In accordance with the present invention, these and other objects are achieved by means of a ground water pressure measuring device which comprises a waterpermeable porous container of resilient sintered plastic material, an inert filling of uniformly sized granular material in the container, a closure for the lower end of the container and a closure for the upper end of the container in which is fixed a flexible tube for transmitting pressure from the interior of the container to a suitable pressure measuring device at the surface. The device is pre-assembled and is adapted to be lowered into a bore hole or installed in an earth structure in direct contact with the soil in which the water pressure is to be measured. The pressure of water entering through the walls of the permeable, porous container is transmitted to the surface through a iiexible tube and may be read off a suitable pressure gauge.

In use, the device is lowered into a bore hole in the ground to a depth at which it is desired to determine the ground water pressure and soil is filled in above. Alternatively, it can be installed in an earth structure, such as an embankment, earth dam or the like during the construction of the structure at a level at which it is desired to measure ground water pressures which may develop during or after the completion of the structure.

The invention is explained in detail hereinafter with reference to the accompanying drawings in which:

FIGURE l is a vertical section showing one embodiment of a pressure measuring device according to the invention; and

FIGURE 2 is a vertical section of a second embodiment of the invention.

Referring to FIGURE l, the device comprises a waterpermeable porous container in the form of a cylinder 1 formed `of a resilient sintered resilient plastic material. The pore size of the plastic material must. be less than 50 microns and preferably in the range of 30 to 50 microns. Plastic material having a smaller pore size, down to 1 micron, for example, can also be used, but such devices tend to respond more slowly to pressure changes. Thus, where rapid response to changes in pressure is desired, the 30-50 micron pore size is preferred. The pores must also :be uniformly sized and interconnected to provide a high degree of water-permeability. We have found that the use of high permeability sintered plastic having the indicated pore sizes for cylinder 1 enables the device to be used in direct contact with all types of soils without danger of plugging. Thus, the necessity of surrounding the device during installation with a sand lilter is eliminated.

Cylinder 1 is closed at the bottom by a disc 2 formed of a suitable plastic material such as polythene and is lilled with inert, uniformly sized granular material 3, such as fine, screened gravel. It is essential to the proper operation or" the device that granular material 3 be uniformly sized. Material comprised of particles of varying sizes tend to change volume when the device is being transported or used resulting in inoperativeness or inaccuracy of the device in use. Uniformly sized filler material 3 comprised of gravel particles within the size range of 1a-inch to 3winch are satisfactory as the filler. Preferably, however, material comprised of generally rounded particles which are all substantially 3s-inch in size is used. This material does not change volume during transportation and use and, also, is sutliciently coarse to permit water to iiow freely through it.

A disc 4 of synthetic plastic mesh is placed over granular ller material 3. The mesh size is selected to ensure that granular material 3 does not pass therethrough. Upper end of cylinder 1 is closed by a plug f5 of polythene or the like and has a hole formed at its centre and reduced portion `6 formed at its outer end. A flexible tube 7 is inserted into the hole in plug 5 and is secured in position by a screw clip 8 surrounding the reduced portion `6 of plug 5. The tube 7 serves for transmitting pressure from the interior of cylinder 1 to a suitable pressure measuring instrument.

FIGURE 2 illustrates the embodiment of the device which is utilized to measure ground water pressure which may develop subsequent to the installation of the device. For example, the device can be installed in an embankment, earth dam or similar structure during its rconstruction for the purpose of measuring ground water pressures Which may develop subsequently. The device shown comprises a porous, resilient sintered plastic cylinder I1, a polythene closure disc 12, a lling of uniformly sized inert granular material 13, a plastic mesh disc 11% and a polythene plug 1S having two holes passing through it. In one hole in plug 5 is inserted a exible tube 16 which terminates above the disc 14 and is intended to be connected to a pressure measuring instrument. In the other hole in disc 15 is inserted a second tlexible tube 17 which passes through the disc 16!- and extends through the filling 13, terminating above the closure disc 12. The

lower end of tube 17 is closed by a plug 18, and a. num-- ber of holes 19 are formed through its wall near to its lower end. A screw clip 2G is used to clamp the plug 1S onto the tubes 16 and 17. Tube 17 may be connected to a water supply and serves for flushing the device to ensure that all air is removed after the ground water rises to the level of its installation and the device becomes operative.

In use, the device, as illustrated in FIGURE l, is lowered, by `means of flexible tube 7, into .a bore hole in the ground in `which it is desired to measure water pressure. The device will normally be utilized where the in-y stallation is below the known level of the water table.

The device of FIGURE 2 is normally employed where the installation is initially above the known level of the water table. It can be lowered into a bore hole by means of ilexible tube 16 or it can be placed in the soil during the construction of an earth structure, In each case, however, the device is placed in direct contact with the soil which is to be tested, and in the case of bore hole installations, the hole above the device is back-lled with soil. No sand iilter is required around the device. In special circumstances, such as where particularly high ground water pressures are encountered or expected, it may be desirable to provide a seal above the device, such as by means of a bentonite clay plug positioned in the bore hole above the device. The ilexible tubes '7 or I6 are connected to a manometer or other suitable pressure measuring device which indicates the ground water pres-1 sure at the bottom of the bore hole. In installations of the device of FIGURE 1 below the level of the water table, the device is operative immediately after installation. In the case of the devices of FIGURE 2 which are installed initially above the `ground water table, the device becomes operative only when the water level rises to the level ofthe installation.

The device shown in FIGURE l may be modified by replacing the solid plug at the lower end by a plug having a hole in which a exible tube is secured similar to that `in plug 5 yat the upper end of the device. This en- 4l ables water to be circulated through to llush the device which then serves the same purpose as the device Shown in FIGURE 2.

What we claim as new and desire to protect by Letters Patent of the United States is:

1. A ground water pressure measuring device for installation in the ground in direct contact therewith comprising a container having closures at each end and a resilient water-permeable porous sidewall formed of sintered plastic material having .a pore size below about 50 microns, an inert lling of uniformly sized granular material in the container for supporting the sidewall thereof, and a flexible tube xed in one end closure for transmitting pressure from the interior of the container to pressure measuring means when the container has been installed in the ground.

2. A device as claimed in claim 1 in `which the con tainer is formed of water-permeable sinte-red plastic material having a pore size in the range of about 30 to 50 microns.

3. A device as claimed in claim 1 in which the iilling consists of uniformly sized rounded gravel particles within the size range of .about 1/s-inch to 3t-inch.

4. A device as claimed in claim 1 including a mesh disc formed of plastic between the granular lling and the upper closure for preventing passage of granular material into the first exible tube.

5. A ground water pressure measuring device for installation in the ground in direct contact therewith cornprising a container' having upper and lower closure means and a resilient water-permeable porous sidewall formed of sintered plastic material having a pore size below about 50 microns, an inert illing of uniformly sized granular material in the container for supporting the side- 'wall thereof, a first flexible tube fixed in the upper end closure for transmitting pressure from the interior of the container to pressure measuring means located remotely from said container and a second ilexible tube xed in the upper end closure and extending to the lower end of the container, said second tube being provided with outlet openings for introducing water into the container from an external source after said container has been installed in the ground.

References Cited by the Examiner FOREIGN PATENTS 444,330 3/1936 Great Britain.

RICHARD C. QUEISSER, Primary Examiner.

J. H. WILLIAMSON, Assistant Examiner. 

1. A GROUND WATER PRESSURE MEASURING DEVICE FOR INSTALLATION IN THE GROUND IN DIRECT CONTACT THEREWITH COMPRISING A CONTAINER HAVING CLOSURES AT EACH END AND A RESILIENT WATER-PERMEABLE POROUS SIDEWALL FORMED OF SINTERED PLASTIC MATERIAL HAVING A PORE SIZE BELOW ABOUT 50 MICRONS, AN INERT FILLING OF UNIFORMLY SIZED GRANULAR MATERIAL IN THE CONTAINER FOR SUPPORTING THE SIDEWALL THEREOF, AND A FLEXIBLE TUBE FIXED IN ONE END CLOSURE FOR TRANSMITTING PRESSURE FROM THE INTERIOR OF THE CONTAINER TO PRESSURE MEASURING MEANS WHEN THE CONTAINER HAS BEEN INSTALLED IN THE GROUND. 